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I killed my fob by jumping in the ocean with it in my pocket.

My car started just fine even though the batt. was dead.

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Discussion Starter #22
How often should the the key remote battery be replaced. I had my previous VW 5 years and never had to replace but it was the switch blade not smart key.
I haven't seen anything on expected battery life but I'd be surprised if it didn't last at least a few years. The key is referred to by Ford as being passive and doesn't actively transmit anything (which would likely be the greatest power drain over time) until it receives a request from one of the three PATS (passive anti-theft system) antennas in the car. This would be at engine start and at some periodic interval afterwards to ensure the key is still in the car, such as when a door is opened.

The shop manual shows the key has to be within three feet of a PATS antenna to be read, so it is likely an extremely small transmitter power for little coded pulse the key has to transmit. Pressing one of the lock/unlock/hatch/panic buttons on the fob would use significantly more transmit power due to range needed away from the vehicle. Also when using the door handle mounted sensors to open the car instead of using the key fob button may also save and prolong battery life since the key can respond with a much lower transmit power to a request from the car to unlock the doors.
 

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Same here. If my VW key was still going strong after 5 this should last longer. Unless they used a subpar battery I suppose.


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RFID tech is apparently being used here. In which the transmitter in the vehicle emits RF radiation (no not the scary stuff) that excites the RFID receiver in the fob. The car is wirelessly powering the fob sort of like that cordless iPhone charger you all saw a few years ago, although at a much smaller power level.

I assume the buttons are the only thing that uses the battery.
 

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Its pretty simple and easy

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For the spare key or battery. It's battery I'm referring too. I think it has to be pried open.


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Ive done both.

I had to replace battery after jumping in ocean with fob in pocket.

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RFID tech is apparently being used here. In which the transmitter in the vehicle emits RF radiation (no not the scary stuff) that excites the RFID receiver in the fob. The car is wirelessly powering the fob sort of like that cordless iPhone charger you all saw a few years ago, although at a much smaller power level.

I assume the buttons are the only thing that uses the battery.
Yes and no. The keys use the 433 Mhz or 315 Mhz band and when you touch the start button or a door handle the car "pings" the key on a frequency. There are probably 4 antenna in the car, and based on the keys ping responses the car knows the physical location of the key. If it's outside on the right, and that door handle was used it unlocks, the same for being on the left with the left door handle. The start button should work if the key is inside the car. The battery does help power that transmitter (that responds to the ping) but it only does so in the form of amplification (as in the op-amp needs the battery). Without the battery the range on the RF is VERY VERY small, hence the slot in the column. There is typically a coil around those slots and with the coil you can detect the miniscule RF range that the unamplified key has.

The buttons on the fob work mostly in reverse, they send the keycode to the car, who verifies the rolling code and then proceeds to unlock or lock the doors. The same was true of the "chipped" key when you stuck the key in the ignition, the RF coil around the key slot communicated with the key to verify that it is indeed learned to that car.
 

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I Am glad I found this
During a sync update ( which frickin weeklY!!!) I got locked out. I eventually got in and got the car started but didn't know about the putting the fob in the hole where the lock used to be.
 

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Just today, I forgot my fob was in my gym bag. I threw the bag in the trunk (which I opened by just using the handle and the RF signal generated from the FOB in the bag), this was mistake number one. I thought for a moment where my fob was...in my bag. But assumed since the fob was now in the car, I would still be able to open the doors. Mistake number two. I went back to the trunk, and you guessed it, mistake number three, it wouldn't open. So there I was... locked out of my ST. I honestly thought it couldn't happen with the FOB physically in the car. :S

The learning point: Leaving the FOB in the front seats..OK. Back seats>>>I don't know. Trunk>>> No Dice.

I have also had issues where I am in the car, someone gets out, I wait for them, make sure the lock button is on Unlock and I still have to open my door first for them to open a door or the trunk..? Anyone else experience this?
 

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First time I took the Blurple Beast to a carwash, the keys were in the front cup holder, engine on. got out to pay, and was locked out. :thumbd: take keys with you always!!
 

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Just today, I forgot my fob was in my gym bag. I threw the bag in the trunk (which I opened by just using the handle and the RF signal generated from the FOB in the bag), this was mistake number one. I thought for a moment where my fob was...in my bag. But assumed since the fob was now in the car, I would still be able to open the doors. Mistake number two. I went back to the trunk, and you guessed it, mistake number three, it wouldn't open. So there I was... locked out of my ST. I honestly thought it couldn't happen with the FOB physically in the car. :S

The learning point: Leaving the FOB in the front seats..OK. Back seats>>>I don't know. Trunk>>> No Dice.

I have also had issues where I am in the car, someone gets out, I wait for them, make sure the lock button is on Unlock and I still have to open my door first for them to open a door or the trunk..? Anyone else experience this?
I did this, I had the keys in a pair of jeans in my bag I was holding and didn't realize they weren't in my pocket. I opened the hatch, put my stuff in and closed it.

Oops.

Somehow though, and I have no idea how, the car knew they were in there and not outside so it popped right back open. Also since it was early in the morning and I didn't know what was going on, I did this 3 times. Luckily the hatch popped back open every single time. Saved me a huge amount of trouble.

Not going to rely on this though, best to keep them on you at all times.
 

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Mine just stays in my pocket. I think that's how they were intended to be used.


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2014 White Focus Titanium with the "automatic manual", not ST but, push button start is the same. My spare key is in the end of the fob. Just about everything listed in the article I have found to be true but my problem goes further. No problems for 30,000 miles then, I stopped to put air in the tires & the car would not start. Would not start with the spare key fob either. Would not remote start. A/C & battery worked. Would not start with fob inserted in plastic cup. The electronic system updated itself remotely according to the display during this process. Eventually showed Key Not In Car Message then put itself into "Transport mode--call dealer" & it turned off the display. The Ford dealer has had the car for a day and a half and has not told me anything yet. I have found the convenience of the keyless, push button start great but the current situation could make me rethink the price of convenience.
 

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Thank you Blackbird for the good info. I have just one question. How do you reprogram the FOB? We lost one FOB and I bought a FOB from the usa, all the numbers inside the FOB match Perfect. Thing is how do I reprogram the FOB any ideas would be great. Thank you Harold
 
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